How to filter out common-mode interference in the sampling loop of an intelligent low-voltage monitoring unit?

The sampling loop employs a high common-mode rejection ratio (CMRR) design for common-mode interference filtering. The front-end uses a CMZ20212A-900T common-mode inductor (90μH), with a common-mode impedance greater than 800Ω at 1MHz. The operational amplifier used is the AD8221 instrumentation amplifier, with a CMRR greater than 100dB (@1kHz). Shielded twisted-pair cables are used for the sampling lines, with the shield grounded at a single point. PCB layout: symmetrical routing at the sampling inputs. The power supply uses an isolated DC-DC module WRB2405S-3W. This design achieves a CMRR greater than 110dB and a sampling error less than 0.1%.